The present invention relates to a light source device for use in, for example, image display apparatus. Particularly, this invention relates to effective cooling of a discharge-lamp light source installed in such a light source device.
Liquid crystal projectors have been introduced as one type of image display apparatus. This type of image display apparatus requires a light source for illuminating a liquid crystal panel (spatial light modulator) that does not emit light. In other words, in this type of image display apparatus, light emitted from a light source device is illuminated onto a liquid crystal panel and modulated thereon. The modulated light is then projected onto a screen to display images thereon.
A light source device for use in this type of image display apparatus has a discharge-lamp light source, such as, a high-pressure mercury lamp, a metal halide lamp or a xenon lamp. It is further equipped with an elliptical reflecting mirror for converging rays of light emitted from the discharge-lamp light source or a parabolic reflecting mirror for reflecting rays of light emitted from the discharge-lamp light source into a parallel beam.
A recent demand for this type of image display apparatus is high intensity of images displayed. High-intensity images require large light output from a discharge-lamp light source. This leads to enhancement of light power for discharge-lamp light sources. For this reason, a fundamental factor in this type of image display apparatus is cooling capacity, the capacity of cooling a discharge-lamp light source.
Higher-intensity images in this type of image display apparatus require lower clearance, one of the specifications for discharge-lamp light sources. This further requires different levels of cooling capacity in accordance with sections of a discharge-lamp light source.
One known type of light source device has an axial-flow fan that guides ambient air to a discharge-lamp light source and cools it with this air. An axial-flow fan is a propeller fan that blows air in the direction parallel to the rotary axis of the fan.
Another recent known type of light source device has a sirocco fan for cooling. A sirocco fan has a multi-blade cylinder that rotates to create airflow in the centrifugal direction from the rotary shaft and a scroll casing that takes the airflow and blows it through an air outflow opening.
A sirocco fan achieves high pressure with effective use of centrifugal force and optimum high static pressure to create a relatively large amount of airflow. It is suitable for local cooling thanks to its airflow directional characteristics and high static pressure.
A light source device is disclosed in Japanese Unexamined Patent Publication No. 2001-125195. In this device, airflow created by a cooling fan is blown into a concave reflector through an air duct. This light source device, however, has an inferior structure with a wide gap (high clearance) between a sirocco fan and a discharge-lamp light source to be cooled by the sirocco fan.
In another light source device disclosed in Japanese Unexamined Patent Publication No. 2002-49098, airflow created by a sirocco fan is blown around a reflector about 1/2 times before guided into the reflector.
In contrast, airflow is blown onto the outer surface of a reflector in still another light source device disclosed in Japanese Unexamined Patent Publication No. 2002-328426.
Due to these inferior structures, the known light source devices are not feasible for cooling a discharge-lamp light source.
In addition, cooling temperatures are the fundamental factors on operating properties in light source devices. In detail, a discharge unit of a discharge-lamp light source requires to be maintained at a relatively high temperature with no excess cooling whereas sealed sections of its both ends require heavy cooling due to, for example, glass-metal junction for the sealed sections.
Moreover, light source devices require precise control of temperature difference inevitably caused by convective airflow within an appropriate range between the upper and lower sections of a discharge unit, for stable operation.
Nevertheless, the known light source devices having the inferior structures discussed above cannot achieve such delicate control.